The DMCA is the Digital Millennium Copyright Act, a U.S. federal law which builds on the Copyright Act to address some of the problems with the infringement of intellectual property on the internet. The primary provisions of the DMCA are an anti-circumvention rule and the internet service provider (ISP) safe-harbor.
The anti-circumvention rule covers the reverse engineering, or ‘cracking’, of encrypted systems. The much more well-known provision is the ISP safe-harbor, which gives a limited immunity against claims of copyright infringement to ISPs who are registered with the Copyright Office as designated agents. ISPs are very broadly defined under the DMCA and can include actual internet access providers and providers of internet services, such as streaming video or photo sharing websites; but, they must register with the Copyright Office to be able to gain the safe-harbor protection.